Just need a suggestion regarding a replacement HDD for this machine.
The 32GB supplied is now no longer sufficient.
Has anyone got any recommendations for a new SD replacement that Windows 10 can be installed on.
I suggest that you review the list of Intel Validated Components for Your NUC. In this list you will find number of HDDs and SSD tested with your NUC. Since you are going to install the Operating System on this drive, better buy SSD (rather than HDD), in order to keep good drive performance.
An additional thing that I would suggest it to add more RAM memory. In addition to 4GB SO DIMM you have already installed, you may add an additional 4GB SO DIMM to increase the total memory to 8GB (Windows will work much better with more RAM). However, buy only the same P/N of SO DIMM you have installed, otherwise, with different SO DIMM modules, your NUC will not work in Double Channel Mode. If you can't find similar memory stick, better buy 2 x 4GB memory kit.